User equipment (UE), also known as mobile stations, wireless terminals and/or mobile terminals are enabled to communicate wirelessly in a wireless communication system, sometimes also referred to as a cellular radio system. The communication may be made e.g. between two user equipment units, between a user equipment and a regular telephone and/or between a user equipment and a server via a Radio Access Network (RAN) and possibly one or more core networks.
The user equipment units may further be referred to as mobile telephones, cellular telephones, laptops with wireless communications capability. The user equipment units in the present context may be portable and enabled to communicate voice and/or data, via the radio access network, with another entity, such as a network node, for example.
The wireless communication system covers a geographical area which is divided into cell areas, with each cell area being served by a network node, radio node or base station e.g. a Radio Base Station (RBS), which in some networks may be referred to as “eNB”, “eNodeB” or “NodeB”, depending on the technology and terminology used. The network nodes may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, typically based on transmission power and thereby also cell size. A cell is the geographical area where radio coverage is provided by the network node/base station at a base station site. One base station, situated on the base station site, may serve one or several cells. The network nodes communicate over the air interface operating on radio frequencies with the user equipment units within serving range of the respective network node.
In some radio access networks, several network nodes may be connected, e.g. by landlines or microwave, to a Radio Network Controller (RNC) e.g. in Universal Mobile Telecommunications System (UMTS). The RNC, also sometimes termed a Base Station Controller (BSC) e.g. in GSM, may supervise and coordinate various activities of the plural network nodes connected thereto. GSM is an abbreviation for Global System for Mobile Communications (originally: Groupe Spécial Mobile).
UMTS is a third generation mobile communication system, which evolved from the GSM, and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. UMTS Terrestrial Radio Access Network (UTRAN) is essentially a radio access network using wideband code division multiple access for user equipment units.
The 3rd Generation Partnership Project (3GPP) has undertaken to evolve further the UTRAN and GSM based radio access network technologies, for example by developing Long Term Evolution (LTE) and the Evolved Universal Terrestrial Radio Access Network (E-UTRAN).
LTE is a technology for realizing high-speed packet-based communication that may reach high data rates both in the downlink and in the uplink. In LTE, network nodes, or base stations, which may be referred to as evolved-NodeBs, eNodeBs or even eNBs, may be connected to a gateway e.g. a radio access gateway, which in turn may be connected to one or more core networks.
In the present context, the expressions downlink, downstream link or forward link may be used for the transmission path from the network node to the user equipment. The expression uplink, upstream link or reverse link may be used for the transmission path in the opposite direction i.e. from the user equipment to the network node.
The possibility to determine the position of a mobile device, or user equipment as it also may be referred to as, has enabled application developers and wireless network operators to provide location based, and location aware, services. Examples of those are guiding systems, shopping assistance, friend finder, presence services, community and communication services and other information services giving the mobile user the information about their surroundings.
In addition to the commercial services, the governments in several countries have put requirements on the network operators to be able to determine, with a certain accuracy, the position of an emergency call. For instance, the governmental requirements in the USA (FCC E911) that it must be possible to determine the position of a certain percentage of all emergency calls with a certain accuracy. The requirements make no difference between indoor and outdoor environment.
Some positioning methods comprise Cell Identification (Cell ID or CID) and Enhanced-Cell ID (E-CID).
Cell ID positioning method comprises, given the cell ID of the serving cell, associating the position of the user equipment with the cell coverage area which may be described, for example, by a pre-stored polygon, where cell boundary is modelled by the set of non-intersecting polygon segments connecting all the corners.
E-CID comprises methods exploiting four sources of position information: the CID and the corresponding geographical description of the serving cell, the Round Trip Time (RTT) with respect to the serving cell, measured e.g. by means of Timing Advance (TA) and/or receive-transmit time difference measured at either user equipment and/or base station side, the CIDs and the corresponding signal measurements of the cells, up to 32 cells in LTE, comprising the serving cell, as well as Angle of Arrival (AoA) measurements.
Angle of arrival (AoA) positioning is a method for determining the direction of propagation of a radio-frequency wave incident on an antenna array. AoA determines the direction by measuring the Time Difference of Arrival (TDOA) at individual elements of the array—from these delays the AoA may be calculated.
The three most common E-CID techniques comprise: CID+RTT, CID+signal strength and AoA+RTT. The positioning result of CID+RTT is typically an ellipsoid arc describing the intersection between a polygon and circle corresponding to RTT. A typical result format of the signal-strength based E-CID positioning is a polygon since the signal strength is subject e.g. to fading effects and therefore often does not scale exactly with the distance. A typical result of AoA+RTT positioning is an ellipsoid arc which is an intersection of a sector limited by AoA measurements and a circle from the RTT-like measurements.
Inter-frequency measurements for E-CID are also possible, and inter-Radio Access Technologies (RAT) measurements have also been discussed. The measurements, such as intra-frequency, inter-frequency, and/or inter-RAT may comprise downlink measurements, uplink measurements, or two-directional measurements such as e.g., RTT, TA or Receiver-Transmitter (Rx-Tx).
A more promising approach may be provided by so-called fingerprinting positioning. Such methods may also be referred to as pattern matching. Fingerprinting positioning algorithms operate by creating a radio fingerprint for each point of a fine coordinate grid that covers the Radio Access Network (RAN). The fingerprint may e.g. comprise the cell IDs that are detected by the terminal, in each grid point; quantized path loss or signal strength measurements, with respect to multiple eNodeBs, performed by the terminal, in each grid point; quantized Timing Advance (TA), in each grid point; quantized AoA information.
Whenever a position request arrives to the positioning node, a radio fingerprint is first obtained (e.g., by requesting and then receiving corresponding measured), after which the corresponding grid point is looked up and reported. This of course requires that the point is unique.
Currently, there is no fingerprinting positioning technology standardized, being viewed as a positioning implementation. However, possible standardization of this group of methods is being discussed in 3GPP. Currently, such methods in LTE rely mainly on E-CID measurements, comprising downlink and/or uplink, intra-frequency, inter-frequency, and inter-RAT, though not limited to them, e.g., the use of Received Signal Time Difference (RSTD) measurements, originally used for Observed Time Difference of Arrival (OTDOA) positioning has also been discussed.
The database of fingerprinted positions or reference positions may be generated in several ways. A first alternative would be to perform an extensive surveying operation that performs fingerprinting radio measurements repeatedly for all coordinate grid points of the RAN. The disadvantages of this approach comprises: the surveying required becomes substantial also for small cellular networks; the radio fingerprints are in some instants, e.g. signal strength and pathloss, sensitive to the orientation of the terminal, a fact that is particularly troublesome for handheld terminals. For fine grids, the accuracies of the fingerprinted positions therefore become highly uncertain. This is unfortunately seldom reflected in the accuracy of the reported geographical result.
Another approach, applied e.g. in Adaptive Enhanced Cell IDentity positioning (AECID), is to replace the fine grid by high precision position measurements of opportunity, and to provide fingerprinting radio measurements for said points. This avoids the above drawbacks, however: algorithms for clustering of high precision position measurements of opportunity needs to be defined and/or algorithms for computation of geographical descriptions of the clusters need to be defined.
The above two problems may be solved by automatically collecting high-precision positions.
Yet another approach is the Observed Time Difference of Arrival (OTDOA) positioning method, which makes use of the measured timing of downlink signals received from multiple radio nodes at the user equipment. With OTDOA, the user equipment measures the timing differences for downlink reference signals received from multiple distinct locations. For each (measured) neighbour cell, the user equipment measures Reference Signal Time Difference (RSTD) which is the relative timing difference between neighbour cell and the reference cell. The user equipment position estimate is then found as the intersection of hyperbolas corresponding to the measured RSTDs. At least three measurements from geographically dispersed base stations with a good geometry are needed to solve for two coordinates of the user equipment and the receiver clock bias. In order to solve for position, precise knowledge of the transmitter locations and transmit timing offset is needed.
To enable positioning in LTE and facilitate positioning measurements of a proper quality and for a sufficient number of distinct locations, new physical signals for positioning have been introduced, i.e. Positioning Reference Signals (PRS), and low-interference positioning subframes have been specified in 3GPP, although OTDOA is not limited to using PRS only and may be performed on other signals as well e.g. Cell-specific Reference Signals (CRS).
Another positioning method is Uplink Time Difference of Arrival (UTDOA). In UTDOA, the uplink positioning makes use of the signals transmitted from the user equipment, wherein the timing of uplink signals are measured at multiple locations by radio nodes, e.g., by Location Measurement Units (LMUs) or eNodeBs (in LTE). The radio node measures the timing of the received signals using assistance data received from the positioning node, and the resulting measurements are used to estimate the location of the user equipment. Position calculation is similar to that with OTDOA.
Another positioning method comprises Global Navigation Satellite System (GNSS) and/or Assisted GNSS (A-GNSS). GNSS is a generic name for satellite-based positioning systems with global coverage. Examples of GNSS systems comprise the American Global Positioning System (GPS), the European Galileo, the Russian Glonass, and the Chinese Compass. GNSS positioning requires GNSS-capable receivers. With A-GNSS, the receivers receive the assistance data from the network. The positioning calculation is based on multi-lateration with Time of Arrival (TOA)-like measurements.
Hybrid positioning is yet another positioning technique that combines measurements and/or positions used by different positioning methods, such as e.g., E-CID measurements or fingerprinting-like approaches, which may also be used for hybrid positioning.
Adaptive Enhanced Cell Identity (AECID) is one kind of fingerprinting positioning technology that refines the basic cell identity positioning method in a variety of ways. The AECID positioning method is based on the idea that high precision positioning measurements, e.g. A-GPS measurements, may be seen as points that belong to regions where certain cellular radio propagation condition persist, i.e., each point may be characterised by a set comprised of cell identity and measurements characterising the environments.
Next, AECID method is described in more detail, by steps 1-4.
Step 1: A-GPS positioning is performed at the same time, and/or within a limited time interval, while the user equipment and/or network perform measurements. The AECID positioning method introduces tagging of high precision measurements according to certain criteria, e.g. comprising:                The cell identities that are detected by the user equipment, in each grid point;        The quantized path loss or signal strength measurements, with respect to multiple radio base stations, performed by the user equipment, in each grid point;        The quantized Round Trip Time (RTT, in WCDMA) or Timing Advance (TA, in GSM and LTE), or UE Rx-Tx time difference (in LTE) in each grid point;        The quantized noise rise, representing the load of a CDMA system, in each grid point;        The quantized signal quality e.g. RxQual in GSM, Ec/N0 in WCDMA and Reference Signal Receive Quality (RSRQ) in LTE;        Radio connection information like the Radio Access Bearer (RAB);        Quantized time.        
It may be noted that the tag comprises a vector of indices, each index taking an enumerable number of discrete values. Continuous variables used for tagging, like path loss, hence need to be quantized.
Step 2: collect all high precision positioning measurements that have the same tag in separate high precision measurement clusters, and perform further processing of said cluster in order to refine it. Geographical region may be smaller than the cell coverage area in the cellular system.
Step 3: A polygon that represents the geographical extension of a cluster is computed, for each stored high precision position measurement cluster. The two most pronounced properties of the algorithm comprise: the area of the polygon is minimized, hence accuracy is maximized, for a given confidence level, and/or the probability that the user equipment is within the polygon, the confidence is precisely known. It is set as a constraint in the algorithm.
Step 4: For an incoming positioning request, the measurement of the user equipment, or the network node is firstly obtained. By looking up cell identities or tags, the polygon corresponding to the determined tag is then looked up in the tagged database of polygons, followed by a reporting, e.g. over Radio Access Network Application Part (RANAP), in UMTS, using the polygon format.
The Architecture and Protocols in LTE will now be discussed. The three key network elements in an LTE positioning architecture are the Location Service (LCS) Client, the LCS target and the LCS Server. The LCS Server is a physical or logical entity managing positioning for a LCS target device by collecting measurements and other location information, assisting the user equipment in measurements when necessary, and estimating the LCS target location. A LCS Client is a software and/or hardware entity that interacts with a LCS Server for the purpose of obtaining location information for one or more LCS targets, i.e. the entities being positioned. LCS Clients may reside in a network node, external node, user equipment, radio base station, etc., and they may also reside in the LCS targets themselves. An LCS Client sends a request to LCS Server to obtain location information, and LCS Server processes and serves the received requests and sends the positioning result and optionally a velocity estimate to the LCS Client. A positioning request may be originated from the user equipment or the network.
Position calculation may be conducted, for example, by a positioning server, such as e.g. E-SMLC or SLP in LTE, or user equipment. The former approach corresponds to either the user equipment assisted positioning mode or network-based positioning, whilst the latter corresponds to the user equipment based positioning mode.
Two positioning protocols operating via the radio network exist in LTE, LTE Positioning Protocol (LPP) and LTE Positioning Protocol-Annex (LPPa). The LPP is a point-to-point protocol between a LCS Server and a LCS target device, used in order to position the target device. LPP may be used both in the user plane and in the control plane, and multiple LPP procedures are allowed in series and/or in parallel thereby reducing latency. LPPa is a protocol between eNodeB and LCS Server specified only for control-plane positioning procedures, although it still may assist user-plane positioning by querying eNodeBs for information and eNodeB measurements. Secure User Plane Location (SUPL) protocol is used as a transport for LPP in the user plane. LPP has also a possibility to convey LPP extension messages inside LPP messages, e.g. currently Open Mobile Alliance (OMA) LPP extensions (LPPe) are being specified to allow e.g. for operator-specific assistance data or assistance data that cannot be provided with LPP or to support other position reporting formats or new positioning methods.
A high-level architecture, as it is currently standardized in LTE, is illustrated in FIG. 1A, where the LCS target is a user equipment, and the LCS Server may comprise an Evolved Serving Mobile Location Centre (E-SMLC) and/or a Service Location Protocol (SLP). In FIG. 1A, the control plane positioning protocols with E-SMLC as the terminating point, and the user plane positioning protocol are schematically shown. In an example implementation, SLP has a proprietary interface with E-SMLC.
As a core network node, logical connections between E-SMLC and Mobile Management Entity (MME) may be made as illustrated in FIG. 1A. E-SMLC may connect to more than one MME and to more than one MME pool.
Uplink positioning architecture may comprise also uplink measurement units such as e.g., Location Measurement Units (LMUs), which may be e.g. logical and/or physical nodes, may be integrated with radio base stations or sharing some of the software or hardware equipment with radio base stations or may be completely standalone nodes with own equipment, including antennas. The architecture may comprise communication protocols between LMUs and the positioning node, some enhancements for LPPa or similar protocols to support uplink positioning.
FIG. 1B illustrates an uplink positioning architecture in LTE, according to prior art.
A new interface, SLm, between the Evolved Serving Mobile Location Centre (E-SMLC), which also may be referred to as a positioning server, or positioning node; and Location Measurement Unit (LMU) is being standardized for uplink positioning. The interface is terminated between a positioning server (i.e. E-SMLC) and LMU. It is used to transport LMUP protocol (new protocol being specified for uplink positioning) messages over the E-SMLC-to-LMU interface. Several LMU deployment options are possible. For example, an LMU may be a standalone physical node, it may be integrated into eNodeB or it may be sharing at least some equipment such as antennas with eNodeB—these three options are illustrated in the FIG. 1B.
The LCS Client is defined as a software and/or hardware entity that interacts with a LCS Server for the purpose of obtaining location information for one or more user equipments. LCS Clients subscribe to a location service in order to obtain location information. LCS Clients may or may not interact with human users. The LCS Client is responsible for formatting and presenting data and managing the user interface (dialogue). The LCS Client may reside in the user equipment or in a Secure User Plane Location (SUPL)-Enabled Terminal (SET), but it may also be at the network side, such as e.g. Public Safety Answering Point (PSAP), a node with network maintenance services, base stations, etc. LCS Client Type is sent in request for positioning estimates to assist a Serving Mobile Location Centre (SMLC) to appropriately prioritize the location request.
The Client Type information is very important in practice since it allows for configuring LCS QoS discrimination in a flexible way. Also, there may exist some restrictions for certain LCS client types.
E.g. in UTRAN, the LCS Client type is signalled in the location reporting control message as one of eight pre-defined values in UTRAN, said values being used to discriminate between different services. The following Client Type values are supported by UTRAN lu interface: Emergency Services, Value Added Services, Public Land Mobile Network (PLMN) Operator Services, Lawful Intercept Services, PLMN Operator Broadcast Services, PLMN Operator Operation and Maintenance Services, PLMN Operator Anonymous Statistics Services, PLMN Operator Target MS Services Support.
It may be noted that there is only one Client Type for commercial Location-Based Service (LBS), i.e. Value Added Services and there is only one Client Type for emergency services. The same set of Client Types is used in LTE.
Service Type is an attribute of specific LBS that may be provided by the LCS client. The LCS Client may also provide the service identity, which may then be mapped by the server to a certain Service Type which may also be verified against the LCS profile and the subscription. The following LCS categories and types have been standardized: Public Safety Services (Emergency Services, Emergency Alert Services), Location Sensitive Charging, Tracking Services (Person Tracking, Fleet Management, Asset Management), Traffic Monitoring (Traffic Congestion Reporting), Enhanced Call Routing (Roadside Assistance, Routing to Nearest Commercial Enterprise), Location Based Information Services (Traffic and public transportation information, City Sightseeing, Localized Advertising, Mobile Yellow Pages, Weather, Asset and Service Finding), Entertainment and Community Services (Gaming, Find Your Friend, Dating, Chatting, Route Finding, Where-am-I), Service Provider Specific Services.
The same set of Service Type (a.k.a. Service Classes) is used in UTRAN and E-UTRAN (LTE).
A positioning result is a result of processing of obtained measurements, including Cell IDs, power levels, received signal strengths, etc., and it may be exchanged among nodes in one of the pre-defined formats. The signalled positioning result is represented in a pre-defined format corresponding to one of the seven Geographical Area Description (GAD) shapes.
Currently, the positioning result may be signalled, in at least one direction, between: LCS target and LCS server, e.g. over LPP protocol, between positioning servers, such as e.g., E-SMLC and Service Location Protocol (SLP), over standardized or proprietary interfaces; between positioning server and other network nodes such as e.g., E-SMLC and any of a Mobility Management Entity (MME); a Mobile Switching Centre (MSC); a Gateway Mobile Location Centre (GMLC); Operations & Maintenance (O&M); a Self-Organizing Network (SON) node; a Mobile Data Terminal (MDT); and/or between the positioning node and LCS Client, e.g., between E-SMLC and PSAP or between SLP and External LCS Client; or between E-SMLC and user equipment. In emergency positioning, LCS Client may reside in PSAPs.
Problems in the prior art solutions comprises difficulties to collect measurements and thus generate reference positions in areas which are not very populated, including rural areas, forests, mountains, off-road areas. Another problem is that insufficient geographical coverage of reference positions is provided in some scenarios, e.g., it takes time to populate the database for areas which are not very populated.
Emergency positioning is particularly important in such less populated areas since it is more difficult to get help in such areas and it may be more difficult to provide a rough description of the location to an emergency operator.
AECID methods are currently not designed to provide positions for low-populated areas or areas with insufficient reference position or reference measurement coverage.
There is no possibility with the current positioning signalling, architecture and positioning node implementation to choose whether unpopulated areas are taken into account or not, neither it is possible to deliver both results and distinguish among them.